Grinding machine

ABSTRACT

This invention relates to a grinding machine and, more particularly, to apparatus for finishing a surface of revolution by the abrasion process wherein a wheel-dressing operation is regulated by a single-finger gage operating on the surface of revolution.

United States Patent Uhtenwoldt et a1. Sept. 5, 1972 [$4] GRINDING MACHINE [72] lnventors: Herbert R. Uhtenwoklt, Worcester; [561 Mm cud Fredrick A. Hohler, Holden; Ed- ED STATES PATENTS mund E. Wlodyka, Saxonville, all of Mass. 2,801,502 8/1957 Blood et a1. ..51/l65.8 3,157,007 11/1964 Lockwood ..51/l65 R 1 Magma Cincinwi Mum-Hui! m 3,299,580 1/1967 Gluchowicz ..51/5 W r e r. M 3,327,432 6/1967 Lockwood ..51 [48 R x 2 'n Jan. 8, 1971 3,534,509 10/1970 l-latstat 81 a1. ..5 "165.8 1 PP No.1 104,859 Primary Banana-Lester M. Swingle MM Us. I n on D. Attorney-Nonnan S. Blodgett (63) Continuation-impart of Ser. No. 796,291, Jan. ABST CT 22, 1969, abandoned. Continuation of Ser. No. This invention relates to a grindin 3 machine and, more 1966 abandoned particularly, to apparatus for finishing a surface of revolution by the abrasion process wherein a wheel- 52 U.S. c1.........................s1/s, 51/50 1-1, 51/165 R dressmg operation is regulated by a singlefinge, gage [51] Int. Cl. .3241) 5/00 operating on the Surface of revolution. [58] Field of Search...51/5, 48 R, 50 R, 50 H, 165 R,

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SHEET 3 BF 6 lllllll 1! "W" i I WWW mvsm'oas HERBER T R. UH TENWOL 0r FREDERICK A. HOHLER EDMUND E. WLODYKA PATENTEB SE? 5 I972 3.688.444

SHEET S I]? 6 i FIGS 5 k. m PRIOR ART .Q] m

news I82 I78 nan FIG. l0

PRIOR ART SHEU 5 BF 6 FINAL SIZE 1a 89 wan! 3| PROFILE 3oz 461,1 my? 9s 1 l 97 T 98 s1 -jl|||| 305 304 1 3 FIG.

GAGE our RETRACT w vM-vE omasssa VALVE GRINDING MACHINE CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of U. S. Pat. application Ser. No. 796,291 filed Jan. 22, 1969 now abandoned which in turn was a continuation of U. S. Pat. application Ser. No. 572,930 filed Aug. 17, 1966, now abandoned.

BACKGROUND OF THE INVENTION In the finishing of workpieces by the grinding method and, particularly, in internal grinding, it is difficult to gage the size of the surface being finished while grinding is taking place. In internal grinding, this is because of the presence of the wheel in the interior of the workpiece. Particularly is it true that the surface is hard to gage when the surface being ground is an internal annular surface, as in the case of grinding the groove on the inside diameter of the outer race of a ball bearing. At the same time, as in all expensive pieces of machinery, it is desirable to use the machine for grinding as much of the time as possible; that is to say, it is desirable to dress the wheel as little as possible while maintaining an adequate surface finish and geometry. Providing for continual examination of geometry of the groove, as well as its surface finish and its size, is a particularly difficult thing to do while the wheel is in the workpiece. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a grinding machine in which dressing of the abrasive wheel takes place only when the wheel has deteriorated to a predetermined extend.

Another object of this invention is the provision of an internal grinding machine having means for dressing the wheel when a predetermined amount of wear has taken place.

A further object of the present invention is the provision of a grinding machine having means for continually measuring the geometry and size of the surface being finished during grinding and correlating the measurement so taken with the need for dressing the wheel.

It is another object of the instant invention to provide a grinding machine having a gage particularly suitable for determining the size of an internal surface of revolution such as a groove while the surface is being ground.

It is a further object of the invention to provide an internal grinding machine having a gage for indicating groove geometry capable of operating while the abrasive wheel is in the bore in the workpiece.

A still further object of this invention is the provision of an internal grinding machine having a gage which is simple in construction, rugged and inexpensive to manufacture, and which is capable of a long life of useful service with a minimum of maintenance.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

In general, the invention consists of a grinding machine for finishing a surface of revolution by means of an abrasive wheel, the machine having a screw-feed mechanism with threadedly engaging members for producing feeding movement between the workpiece and the abrasive wheel and with an arm rotatable therewith. A wheelwear sensor switch is engageable on occasion by the said arm. A single-finger gage is movable into operative position with the surface of revolution. Control means is connected to the switch and the gage and is operative to bring about a dressing operation when the switch is engaged before the gage indicates a final size of the surface of revolution.

The character of the invention, however, may be best understood by reference to one of its structural forms as illustrated by the accompanying drawings in which:

FIG. 1 is a plan view of a grinding machine embodying the principles of the present invention,

FIG. 2 is a front view of the machine with portions broken away along the line II-ll OF FIG. 1 for clarity of presentation,

FIG. 3 is a transverse elevational view taken along the line III-III of FIG. I of a gage forming part of the machine,

FIG. 4 is an inclined view of the gage taken along the line IV-IV of FIG. 3,

FIGS. 5, 6, and 7 are sectional views of the gage taken on the lines V-V, Vl-VI, and VII-VII, respectively, of FIG. 3,

FIG. 8 is a schematic view of the control circuitry associated with the invention,

FIG. 9 is a plan view of the prior art grinding machine disclosed in US. Pat. No. 3,534,509 of Oct. 20, 1970,

FIG. 10 is a schematic view of the hydraulic circuitry used in the prior art machine, and

FIG. 11 is a schematic view of a control means forming part of the present invention.

Referring to FIG. 1, wherein are best shown the general features of the invention, the grinding machine, indicated generally by the reference numeral 10, is shown as consisting of a base 11 having a flat horizontal upper surface on which are mounted a workhead I2 and a wheelhead 13. The workhead is carried on a workhead table 14 which is mounted for longitudinal motion on the base by means of ways 15. Similarly, the wheelhead I3 is carried on a wheelhead table 16 which is mounted for transverse sliding motion on the base I I by means of ways 17. Extending between the workhead table 16 and the base 11 is a feed cylinder 18 which is suitably provided with fluid pressure to bring about movement of the table I6 transversely of the base. Similarly, a hydraulic cylinder 19 connects the table 14 to the base 11 and brings about longitudinal movement of the table 14 over the ways 15. Extending from the wheelhead 13 is a rotatable spindle 21 carrying on its outer end an abrasive wheel 22. Carried by the workhead 12 and rotated thereby is a workpiece 23; for the purpose of illustration, this workpiece is shown as the outer race of a ball bearing whose inner groove is being ground by the abrasive wheel 22. The workpiece is supported on its outer cylindrical surface by shoes in the usual way and rotatably driven by the workhead l2. Residing in the bore of the workpiece during the grinding operation is a pneumatic air gage 24 which will be described more fully hereinafter.

The amount of air that is able to pass between the surface of the gage and the surface of the groove in the workpiece is an indication of the workpiece size, and

this flow is transmitted to a control box which contains various pressure switches to operate electrically to open and close solenoid valves in the hydraulic circuitry of the machine.

Slidable on the upper surface of the base 11 is a block 26 which, at its rearward end, is threadedly attached to a threaded shaft 27 which, in turn, is driven by a motor 28 fastened to the base 11. This motor is the type capable of small rotary increments in response to pulses received from an electrical control. By regulating the number and nature of the pulses from the electrical control, it is possible to rotate the motor quickly or slowly in exact amounts to make the block 26 move transversely over the surface of the base 11. In the present apparatus, this motor is used to produce a compensation dress and to provide for a retraction of the wheel at a suitable time in the grinding cycle, as is well known. A dressing apparatus 29 is mounted on the workhead table 14 in position to engage the wheel 22 at a suitable time in the grinding cycle.

The block 26 is provided with a transverse slot 31, and in this slot resides a horn 32 extending downwardly from the undersurface of the wheel head table 16. The front of the block is provided with a hardened metal insert 33. Mounted on the front portion of the wheelhead table 16 is a retractable stop 14 having a contact rod 35 extending toward the block 16 and toward the metal insert 33. Mounted at the front of the retractable stop is a gear 36 and, to the right, (in FIG. 2) is an adjusting knob 37.

Referring now to FIG. 2, it can be seen that the gear 36 is attached to the outboard end of the rod 35 and that the gear is contacted by a feedback mechanism 38. This feedback mechanism consists of a housing 39 having a bore 41 in one end of which is slidably carried a piston 42. A conduit 43 is connected to the extreme end. Similarly, the other end of the housing is provided with a bore 44 carrying a piston 45, the bore being connected to a conduit 46. Connected to the pistons 42 and 45 are pawls 47 and 48, respectively, arranged to contact the ratchet wheel or gear 36 on occasion. A spring-loaded plunger 49 is mounted in the housing 39 and engages the teeth of the gear to prevent rotation by vibration.

Forming part of the retractable stop 14 is a housing 51 through which extends a bore 52 slidably carrying a piston 53. Connected through the housing to the left end of the bore 52 is a conduit 54. Also connected to the housing is a conduit 55 connected into a passage leading through an adjustable throttle 56 which is controlled by the knob 37) to the right-hand end of the bore 52.

Extending rearwardly from the center portion of the piston 53 is a rod 58. This rod is pivotally mounted in the top of a crankarm 59 whose other end is connected through a sleeve to the contact rod 35. The forward end of the slot 31 in the block 26 is provided with a hardened metal button 30 adapted to engage on occasion a similar hardened metal button 30 located on the forward surface of the horn 32. The crank arm 59 is provided with a laterally extending finger 72 having a hardened metal button 73 adapted to contact a wheel wear sensor switch 25. The switch is mounted in the housing 34 and is provided with a downwardly extending rod 74 which is vertically slidable and held in a downward position by a coil spring. At the upper end, the switch 25 includes a microswitch 57 having a thin actuating rod 62 which is capable of being engaged by the slidable rod 74 on occasion. The switch 57 is threadedly engaged with the housing and is provided at the upper end with an adjusting knob 75.

As is evident in FIG. 3, the apparatus is provided with a profile sensing device 61 which operates in the workpiece while grinding is taking place.

Referring now to FIGS. 3 and 4, it can be seen that the workpiece 23 is supported on its outer cylindrical surface by means of a 3 oclock shoe 63 and a 6 oclock shoe 64. The profile sensing device 61 has a rotating rod 65 which enters the workpiece 23 and has a dependent finger 66 which is rotated in a semi-circular path in the groove in the workpiece. It has an element which communicates the character of the surface (particularly with regard to its geometry) back to the main body of the device. The air gage 24 is provided with a base 67 by which is is mounted on the machine base. This base is provided with two extensions 68 and 69 having a space between them in which lies the gage mount 71 for rotational motion about an inclined hinge pin 76. Supported by the gage mount is the gage finger 77 which means provided for longitudinal adjustment. Out of the top of the gage finger extends a conduit 78 providing air for a suitable gaging nozzle at the end of the finger which resides in the workpiece 23.

In FIG. 5 it can be seen that the body 67 of the gage is provided with a transverse bore 79 in which is slidably carried a piston 81. A pressure oil conduit 82 enters the outer end of the bore for operating the piston 81. Opposed to the piston and pressing on the other side of the gage mount 71 is an adjustable stop screw 80. in FIG. 7 it can be seen that the body 67 also has a bore 83 carrying a piston 84 which engages the other side of the hinged gage mount 71 and drives it against an adjustable stop screw 85 under the impetus of pressure oil received from a conduit 86 connected to the outer end of the bore 83. Located between the lines of action of the two pistons 81 and 84 is an air jet 87 supplied with air through a conduit 88. this being used as an interlock control to assure that the gaging finger is out of the workpiece before the table is moved out and also before unloading and re-loading of the grinding machine is attempted.

FIG. 8 is a schematic view of the controls contained in the grinding machine. Referring to this figure, it can be seen that the air-gage 24 is connected by the conduit 78 to a control 89 which contains a pneumatic Wheatstone bridge in the usual manner in one branch of which resides the nozzle on the finger 77. The control develops an electrical signal indicative of the gap between the gage and the surface of the groove in the workpiece 23. This electrical signal is imposed on an electrical line 91 connected to a main control 92. Similarly, the profile-sensing device 61 scans the surface of the groove from side to side and provides a signal through the conduit 93 to a control box 94 which converts the pneumatic signal developed between the end of the finger 66 and the workpiece surface to an electrical signal which it furnished to a conduit 95 leading to the main control 92. The switch 57 is operated by the finger 72 at a certain stage of the proceedings and the closing of this switch is felt through the lines 96 and 97 by a control 98 having an output line 99 leading to the main control 92. The main control is of the conventional type used in internal grinding machines for carrying out an automatic cycle and is similar to that shown in the US. Pat. of Robert G. Hatstat et al, No. 3,534,509 assigned to the same assignee as the present application.

Referring now to FIG. 9, wherein are best shown the general features of the prior art, the grinding machine, indicated generally by the reference numeral 110, is shown as consisting of a base 111 having a flat horizontal upper surface on which are mounted a workhead 112 and a wheelhead 113. The workhead is carried on a workhead table 114 which is mounted for longitudinal motion on the base 111 by means of ways 115. Similarly, the wheelhead 113 is carried on the wheelhead table 116 which is mounted for transverse sliding motion on the base 111 by means of ways 117. Extending between the workhead table 116 and the base 111 is a feed cylinder 118 which is suitably provided with fluid pressure to bring about movement of the table 1 16 transversely of the base. Similarly, a hydraulic cylinder 119 connects the table 114 to the base 111 and brings about longitudinal movement of the table 114 over the ways 1 l5.

Extending from the wheelhead 113 is a rotatable spindle 121 carrying on its outer end an abrasive wheel 122. Carried by the workhead 112 and rotated thereby is a workpiece 123: for the purpose of illustration, this workpiece is shown as the race of a ball bearing. The inner bore is being ground by the abrasive wheel 122 and the workpiece is supported on its outer cylindrical surface. Residing in the bore of the workpiece during the grinding operation is a pneumatic air gage 124 of the well known type which gage is connected to a control box 125. The control box 125 provides a flow of air to the gage 124 in a well known manner. The amount of air that is able to pass between the surface of the gage and the surface of the bore of the workpiece is an indication of the workpiece size and this flow is transmitted to the control box 125 which contains various pressure switches to operate electrically to open and close solenoid valves in the hydraulic circuitry of the machine.

Slidable on the upper surface of the base 111 is a block 126 which, at its rearward end, is threadedly attached to a threaded shaft 127 which, in turn, is driven by a motor 128 fastened to the base 111. This motor is of the type capable of small discreet rotary increments in response to pulses received from an electrical control. By regulating the nature and number of the pulses from the electrical control, it is possible to rotate the motor quickly or slowly in exact amounts to make the block 126 move transversely over the surface of the base 111. In the present apparatus, this motor is used to produce compensation after dress and to provide for retraction of the wheel at a suitable time of the grinding cycle, as is well known. A dressing diamond 129 is mounted on the workhead table 114 in position to engage the wheel 122 during a dressing traverse at a suitable time in the grinding cycle.

The block 126 is provided with a transverse slot 131 and in this slot resides a horn 132 extending downwardly from the undersurface of the wheelhead table 116. The front of the block 126 is provided with a hardened metal insert 133. Mounted on the front portion of the wheelhead table 116 is a retractable stop 134 having a contact rod 135 extending toward the block 126 and toward the metal insert 133. Mounted at the front of the retractable stop is a gear 136 and to the right (in FIG. 2) is an adjusting knob 137.

Referring now to FIG. 10, which shows the hydraulic circuitry in the machine, the oil for the circuitry is provided by a pump 176 driven by a motor 177. The pump is connected to a line 178 adapted to carry 500 psi unfiltered oil. The pump is also connected through a filter 179 to a line 181 adapted to carry a 500 psi filtered oil. The pump is also connected through a pressure regulating valve 182 which provides filtered oil at 125 psi to a line 183. Extending through the circuitry is a 5 psi drain line 184 and a main drain line 185. The pressure lines 178, 181 and 183 operate with the drain lines 184 and 185 to regulate various cylinders in the machine, including the workhead table cylinder 119 which has been described in connection with FIG. 9. Also included in the circuitry is a TABLE IN dashpot 186, a TABLE OUT dashpot 187, a LOADING cylinder 188, the FEED cylinder 118 (which has also been described in connection with FIG. 9), a RETRACTABLE STOP PRE-LOAD cylinder 189, a WHEELHEAD SWIVEL cylinder 191, the GAGE IN cylinder 192, another GAGE IN cylinder 193, and DIAMOND TURNER cylinders 194 and 195. Regulating the flow of pressure fluid from the pressure lines 178, 181 and 183 to those cylinders and to the drain lines 184 and 185 are the following solenoid valves: TABLE INDEX valve 196, a speed valve 197, a load valve 198, a FEED AND RETRACT valve 199, a pressure-regulating valve 201 for producing low pressure fluid and a pressure-regulating valve 202 for producing high pressure fluid, the HIGH-LOW FORCE CROSS-SLIDE valve 203, a CROSS-SLIDE FEED valve 204, a BACK-OFF valve 205, a DAMPER BY-PASS valve 206, as well as WHEELHEAD SWIVEL valve 207, the SINGLE-JET GAGE valve 208, the DOUBLE JET GAGE valve 209, a DIAMOND TURNER valve 211, a FEED-BACK valve 212, and another FEED-BACK valve 213. It 212 and 213 are connected to the conduits 143 and 146 leading to the feed-back mechanism 138. Associated with the piston 153 and its bore 152 is the throttle 156 and the check valve 157.

FIG. 11 shows the control means associated with the grinding machine. The signal from the final size gage 24 arrives in the conduit 78 at the control 89 and its ope rative on a normally open pressure switch 301. When the final size is reached, the closure of the switch 301 completes a circuit in the line 91 to the main control 92. Similarly, a signal from the profile-sensing device 66 arrives in the conduit 93 at the control 94 which contains a sweep band 302 capable, when the signal reaches a predetermined value, of contacting the contactor 303 and closing the switch. This closure completes a circuit in the line 95 leading to the main control 92. When the switch 57 is closed, it serves to complete a circuit in the control 98 between an electri cal source 304 and the coil of a normally-open relay 305. When the relay 305 is closed in this manner, it completes a circuit in the line 99 leading to the main control 92. When the GAGE OUT on jet 87 indicates by pressure in the conduit 88 that the gage is removed from the bore in the workpiece, the pressure switch 306 in the control 89 completes a circuit in the line 307 leading to the main control.

The main control 92 consists in part of the RET'RACT valve 199 which is operative to back the wheel away from the surface of the workpiece, the DRESSER valve 211 which is operated to bring the dresser into position to dress the wheel, and the TABLE INDEX valve 196 which serves to move the workpiece away from the wheel and to position the dresser adjacent the wheel for a dress. The line 307 operates in conjunction with an electrical power source 308 and a relay 309 to assure that the TABLE INDEX valve is inoperative unless the gage is out of the bore. The line 91 cooperates with the source 308 to energize a relay 311 when final size is reached, but normally does not operate the DRESSER valve 211; normally, therefore, at the end of the grinding cycle dressing would not take place, but the cycle would be terminated. When the line 95 is closed (by poor surface finish in the workpiece) the DRESSER valve is energized as well as the other valves and dress takes place. If the completion of the circuit in the line 99 takes place before the completion of the circuit in the line 91, this fact indicates that the wheel is dull; the dresser valve 211 will be activated as well as the other valves.

An end of the grinding cycle will, therefore, consist of the following steps:

1. Starting at finish size, the gage will be retracted and the cross-slide will back off.

2. The table will move out.

3. Dress will take place, if required.

4. workpiece will be unloaded and a new workpiece loaded.

5. Table will move in again.

6. The cross-slide will feed in.

7. The gage will be introduced into the bore, at Step 3, the dressing cycle will be set in motion only if:

A. The surface finish Rl-lS exceeds a present quantity, or

B. If the switch 57 is closed before the gage 24 indicates that final size is reached.

The operation of the apparatus will now be readily understood, in view of the above description. The machine operates through a standard grinding cycle, the wheel advancing at a low force rate on a new workpiece which has just been loaded in the machine. The cylinder 19 has previously moved the workhead table 14 toward the wheelhead table 16 so that the wheel 22 lies within the bore of the workpiece 23. Transverse movement takes place under the impetus of the cylinder 18 on a rapid traverse movement. At a certain point the wheel contacts the workpiece and grinding takes place at a low force rate. This low force rate is brought about by the introduction of oil into the feed cylinder 18 by its connection to a pressure-reducing valve giving low pressure oil. The length of time that the low force grinding takes place may be determined by a timer. At that point a high force grinding operation begins. At a certain point the contact rod 35 contacts the block 33 and a feed valve is energized to start the feed cylinder to grind at a pre-determined rate to a first gage size. That is to say, the gage 24 eventually determines that the grinding operation has progressed to the point where the workpiece bore has been enlarged to a first size. At that time, the gage control 89 operates through the main control 92 to start a sparkout timer. No feed takes place, but the residual deflection in the spindle continues the grinding operation. If dressing is not to take place, the wheel moves on a traverse to bring the wheel into the bore of the workpiece and the wheel moves on rapid traverse without grinding the material. At this point, the inner end of the contact rod 35 contacts the hardened metal insert 33 on the block 26. The cylinder 18 presses the table rearwardly attempting to move the wheel into further contact with the workpiece. However, the table is unable to go any further because of the retractable stop 34 and its contact rod 35. The feed cylinder represented by the piston 53 and the bore 52 moves to the right carrying the crankarm 59 with it, which causes the contact rod 35 to move outwardly, thus permitting the wheelhead table 16 to move rearwardly and move the wheel into the workpiece on a grinding operation. This continues for a while to bring about a feed rate grinding operation. The gage 24 indicates when the workpiece approaches the finish size and stops the operation of the piston 53 at a certain point. From then on, grinding takes place on a sparkout operation. The gage 24 indicates the final size and orders the wheel to retract. The wheel, of course, moves out of the workpiece in order to change workpieces.

The gage finger 77 is moved in and out of the workpiece at the proper time in the cycle by the operation of the piston 81 under the impetus from the conduit 82 and the impetus of the piston 84 operating under the oil from the conduit 86. The air jet 87 operating under air from the conduit 88 on the gage mount 71 assures that the gage is out of the hole in the workpiece before any attempt to traverse the machine takes place. This is mainly to permit loading and unloading of the workpiece.

If the arm 72 contacts and closes the switch 57 before the gage 24 indicates that the workpiece surface has reached its final size, this indicates that the wheel is worn and in poor condition and needs to be dressed. At that time, the main control senses this condition and causes a dressing operation to take place. In most of the successive grinding cycles, however, the wheel will not be dressed. At the same time, the profile-sensing device 6] indicates also when the surface of the groove is out of correct geometric shape and indicates this through the control 94 to the main control 92 to bring about a dress also.

it should be noted that the pivoting of the single finger gage 24 takes place around the axis of the pivot pin 75. This pivot pin is well outside of the plane of the groove in the workpiece 23 so that the pivoting of the finger 77 about this pivotal axis permits the gage to move in and out of the workpiece without difficulty and to remain in the workpiece while the wheel 22 is in the workpiece grinding. There is a crescent-shaped space between the periphery of the wheel 22 and the back surface surface of the interior of the workpiece and the gage 24 operates in this area as does the profile-sensing device 61. The gage 77 operates on a specific part of the workpiece, namely, along a line passing through the center of the workpiece at a right angle to a bisector of the Vee formed by lines joining the contact points with the shoes 63 and 64 to the center of the workpiece. The advantages of this gaging position are shown and described in the US. Pat. of Lockwood No. 3,157,007.

lt is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent 1s:

1. A grinding machine for finishing a surface of revolution of a workpiece by means of an abrasive wheel, comprising a. a screw-feed mechanism having threadedly engaging members for producing feeding movement between the workpiece and the abrasive wheel and having an arm rotatable therewith,

b. a wheelwear sensor switch engageable on occasion by the said arm,

c. a single-finger gage movable into operative position with the surface of revolution, and

d. control means connected to the said switch and the said gage, the control means being operative to bring about a dressing operation when the said switch is engaged before the said gage indicates a final size of the surface of revolution.

2. A grinding machine as recited in claim I, wherein a profile indicator is mounted adjacent the workpiece and operative to scan the said surface of revolution, the indicator being connected to the said control means, whereby the control means brings about a dressing operation when the indicator finds that the geometry of the said surface of revolution has deteriorated beyond a predetermined amount.

3. A grinding machine as recited in claim 2, wherein the said profile indicator scans the surface of revolution by sweeping in a plane parallel to the axis.

4. A grinding machine as recited in claim 3, wherein the surface of revolution is annular and the indicator sweeps in an arc extending across the annulus.

5. A grinding machine as recited in claim wherein the single-finger gage is pivotally mounted for rotation from a first position in which the end of the finger is away from the said surface to a second position adjacent the surface, the rotation taking place about an axis lying in a plane at a right angle to the axis of the surface and spaced longitudinally off the axis a substantial distance from the surface.

6. A grinding machine for finishing an internal surface of revolution of a workpiece by means of an abrasive wheel, comprising a. a workhead for supporting and rotating the workpiece,

b. a wheelhead having a rotatable spindle adapted to carry at its end an abrasive wheel,

c. a screw-feed mechanism having threadedly engaging members for producing feeding movement between the workpiece and the abrasive wheel and having an arm rotatable therewith,

. a wheel wear sensor switch engageable on occasion by the said arm,

. a gage having a main body mounted adjacent the wheelhead and having a finger with a pneumatic gaging nozzle at its outer end, the finger being pivotally attached to the main body for swinging motion about an axis which is substantially spaced from the surface of revolution in the direction of th ma'or axis of the said surface a me actuator means associated with the mam body for bringing about the said swinging motion of the finger from a first position in which the nozzle lies within the workpiece adjacent the said surface to a second position in which the finger is entirely removed from the workpiece, and

g. control means connected to the said switch and the said gage, the control means being operative to bring about a dressing operation when the said switch is engaged before the said gage indicates a final size of the surface of revolution.

7. A grinding machine as recited in claim 6, wherein a profile indicator is mounted adjacent the workpiece and operative to scan the said surface of revolution, the indicator being connected to the said control means whereby the control means brings about a dressing operation when the indicator finds that the geometry of the said surface of revolution has deteriorated beyond a predetermined amount, the said profile indicator scanning the surface of revolution by sweeping in a plane parallel to the axis, and the surface of revolution being annular and the indicator sweeping in an are ex tending across the annulus.

i l t l 

1. A grinding machine for finishing a surface of revolution of a workpiece by means of an abrasive wheel, comprising a. a screw-feed mechanism having threadedly engaging members for producing feeding movement between the workpiece and the abrasive wheel and having an arm rotatable therewith, b. a wheelwear sensor switch engageable on occasion by the said arm, c. a single-finger gage movable into operative position with the surface of revolution, and d. control means connected to the said switch and the said gage, the control means being operative to bring about a dressing operation when the said switch is engaged before the said gage indicates a final size of the surface of revolution.
 2. A grinding machine as recited in claim 1, wherein a profile indicator is mounted adjacent the workpiece and operative to scan the said surface of revolution, the indicator being connected to the said control means, whereby the control means brings about a dressing operation when the indicator finds that the geometry of the said surface of revolution has deteriorated beyond a predetermined amount.
 3. A grinding machine as recited in claim 2, wherein the said profile indicator scans the surface of revolution by sweeping in a plane parallel to the axis.
 4. A grinding machine as recited in claim 3, wherein the surface of revolution is annular and the indicator sweeps in an arc extending across the annulus.
 5. A grinding machine as recited in claim -, wherein the single-finger gage is pivotally mounted for rotation from a first position in which the end of the finger is away from the said surface to a second position adjacent the surface, the rotation taking place about an axis lying in a plane at a right angle to the axis of the surface and spaced longitudinally off the axis a substantial distance from the surface.
 6. A grinding machine for finishing an internal surface of revolution of a workpiece by means of an abrasive wheel, comprising a. a workhead for supporting and rotating the workpiece, b. a wheelhead having a rotatable spindle adapted to carry at its end an abrasive wheel, c. a screw-feed mechanism having threadedly engaging members for producing feeding movement between the workpiece and the abrasive wheel and having an arm rotatable therewith, d. a wheel wear sensor switch engageable on occasion by the said arm, e. a gage having a main body mounted adjacent the wheelhead and having a finger with a pneumatic gaging nozzle at its outer end, the finger being pivotally attached to the main body for swinging motion about an axis which is substantially spaced from the surface of revolution in the direction of the major axis of the said surface, f. a linear actuator means associated with the main body for bringing about the said swinging motion of the finger from a first position in which the nozzle lies within the workpiece adjacent the said surface to a second position in which the finger is entirely removed from the workpiece, and g. control means connected to the said switch and the said gage, the control means being operative to bring about a dressing operation when the said switch is engaged before the said gage indicates a final size of the surface of revolution.
 7. A grinding machine as recited in claim 6, wherein a profile indicator is mounted adjacent the workpiece and operative to scan the said surface of revolution, the indicator being connected to the said control means whereby the control means brings about a dressing operation when the indicator finds that the geometry of the said sUrface of revolution has deteriorated beyond a predetermined amount, the said profile indicator scanning the surface of revolution by sweeping in a plane parallel to the axis, and the surface of revolution being annular and the indicator sweeping in an arc extending across the annulus. 